1. Field of the Invention
The present invention relates to an antenna, and more particularly, to an antenna that is operational at dual frequency bands, and having compact size for wireless communication.
2. Description of the Prior Art
Wireless communication, as the term itself implies, needs no cables, fibers or wires to relay signals. This unique feature makes wireless communication an important technology for all communication systems. As the xe2x80x9cglobal villagexe2x80x9d forms, everyone wants to have convenient access to more information. Portable communication devices based on wireless communication, such as mobile phones, meet that needs.
An antenna used to transmit and receive radio signals is the key element in wireless communication. Antennas must be of high quality and compact according to portable communication device requirements. Moreover, to expand signal transmission capacity, radio signals are modulated with different carrier frequencies, so that the signals can be transmitted via different frequency bands. Also, radio signals with high information density (measured by xe2x80x9ctransmitted bytes per secondxe2x80x9d in some systems) widen the bandwidth of the frequency band in modern wireless communication systems. These additional requirements make a modern antenna preferably operative at more than one frequency band with broad bandwidth.
Please refer to FIG. 1. FIG. 1 illustrates a prior art planar antenna 10 disclosed in U.S. Pat. No. 5,926,139. The antenna 10 has two conductive plates 12 and 14, the plate 14 being the ground plate. A signal feeder (not shown) is electrically connected to a contact point 16 on the plate 12, and a pin connector 18 connects the plates 12 and 14. A J-shape slot is cut in the plate 12 to form two parts 17A and 17B connected at the end of the slot. Each of the two parts 17A and 17B corresponds to a frequency band, making the prior art operative in dual frequency bands. However, as the area of the portion connecting parts 17A and 17B at the end of the slot corresponds to the effective bandwidth of the antenna 10, the prior art antenna suffers from narrow bandwidth.
Therefore, it is an objective of the present invention to provide an antenna that is capable of operating at dual frequency bands with broad bandwidths, yet remains compact in size. Embodiments disclosed in the present invention can be divided into two major forms. The former has a ground plate and a first plate; the latter has a ground plate and a folded structure which is formed by a first plate, a second plate above the first plate, and conductive connectors connecting the first plate and the second plate.
It is a further objective of the present invention to disclose a well-dimensioned embodiment with the folded structure capable of operating at frequency bands specified by GSM (Global System for Mobile communication technical specifications) 900 and GSM 1800.
It is also an objective of the present invention to disclose a method of manufacturing and assembling the embodiment with the folded structure.
In accordance with the claimed invention, the present antenna includes a conductive ground plate, and a conductive first plate and a signal feeder. The first plate is set above the ground plate, with a first distance separating the first plate from the ground plate. The first plate has two slots extending from two edges of the first plate. The two extending points of the two slots are located approximately opposite to each other around a central portion of the first plate. Furthermore, an embodiment with two plates forming a folded structure set above the ground plate is disclosed in the present invention. The folded structure has a first plate and an additional second plate, of the same shape as the first plate. The second plate is set above the first plate and a second distance separates the two plates. Conductive connectors are used to connect the first plate and the second plate.
It is an advantage of the present invention that the antenna is operative at dual frequency bands, with broad bandwidths, without compromising the compactness of size.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.